Beat peanut butter and cream cheese on medium-high speed with an electric mixer until smooth and creamy. Beat in sugar until well blended. Beat in cream and egg until smooth.

Preheat oven to 350°F. Grease (with shortening) a 10-inch (12-cup) Bundt pan and dust with cocoa powder, tapping out excess.

Combine sour cream, oil, milk, vanilla, and eggs in a large bowl; beat on low speed with an electric mixer until smooth. Add cake mix and pudding mix (do not add additional ingredients that are called for on the package for the cake and pudding mixes); beat on medium speed for 2 minutes. Fold in peanut butter cups.

Pour half of batter into prepared pan. Spoon peanut butter filling evenly onto center of batter. (Do not let filling touch the sides of pan.) Pour remaining batter over filling. Tap pan gently on counter to remove air bubbles.

Bake in preheated oven until a wooden pick inserted in center comes out clean, 50 to 55 minutes. Cool in pan on a wire rack 10 minutes. Remove from pan to wire rack; cool completely, about 1 hour.

Whisk together peanut butter and milk in a small bowl until smooth; whisk in powdered sugar until blended. Spoon glaze over cake. Refrigerate uncovered until glaze is set, about 15 minutes.

Place chocolate morsels in a small bowl. Bring cream, peanut butter, and corn syrup to a simmer in a small saucepan over medium heat, stirring constantly. Pour over chocolate morsels; let stand 2 minutes. Whisk until smooth. Spoon over cake and Peanut Butter Glaze. Refrigerate uncovered 10 minutes or until glaze is almost set. Garnish with chopped peanut butter cups.